A photovoltaic device is an element which converts light energy to electrical energy and is utilized as for example a solar cell. As an example of such a solar cell, silicon-based solar cells or compound semiconductor solar cells may be mentioned, but recently dye-sensitized solar cells, which can be produced cheaper than these solar cells, are becoming the focus of attention. However, a dye-sensitized solar cell is an electrochemical cell, so an organic electrolyte or ionic liquid is used as an electrolyte (for example see U.S. Pat. No. 4,927,721). When using an organic electrolyte, there is the problem that the energy conversion efficiency ends up falling during long term use due to evaporation and depletion. Further, when using an ionic liquid as the electrolyte, while it is possible to prevent evaporation and depletion over long term use, there is a problem of leakage (for example see WO95/18456). It is also known to use a substantially organic solvent-free solid or gel-like organic electrolyte for the electrolyte of a photo-electrochemical cell (for example see Japanese Unexamined Patent Publication (Kokai) No. 2002-298935).
It is known to obtain a conductive polymer containing electrolyte ions as a dopant by chemical oxidative polymerization of aniline or an aniline derivative. However, a conductive polyaniline is generally insoluble in an organic solvent and non-melting and therefore, is inferior in shapeability and difficult to develop applications thereof. Further, it has been reported to obtain polyaniline and polyaniline derivatives soluble in an organic solvent by polymerization of a salt of an aniline comprising sulfonic acid such as dodecylbenzene sulfonic acid, dinonylnaphthalene sulfonic acid and aniline or its derivative (Japanese Unexamined Patent Publication (Kokai) No. 6-279584 No. 2003-176409, U.S. Pat. No. 5,232,631). However, the solubility of polyaniline or a polyaniline derivative in an organic solvent is not necessarily high. For example, the solubility of aniline dodecylbenzene solfonate in toluene or xylene is at most 0.5%. Thus, a method for producing polyaniline having a further higher solubility is sought. Further, a conductive polymer composition comprised of a substituted or unsubstituted polyaniline, protonic acid, and organic solvent has been reported (for example see Japanese Unexamined Patent Publication (Kokai) No. 2003-176409), but the oxidizing agent/aniline (molar ratio) at the time of polymerization of the aniline is 0.5, so there is the problem that the yield of the polyaniline is 30 to 40%. If making the oxidizing agent/aniline (molar ratio) 1.0 or more, there is the problem that the dispersion stability becomes insufficient.
A photovoltaic device is composed of a photoelectrode and a counter electrode. In the past, as the counter electrode, an electrode composed of a platinum thin film formed on a transparent conductive glass substrate by vacuum vapor deposition or sputtering has been used. However, vacuum vapor deposition or sputtering requires expensive vacuum equipment. Further, the size of the substrate is strictly restricted, so it is difficult to form a platinum layer on a substrate of a large area.
The dye-sensitized solar cell was developed by M. Graetzel et al. of Switzerland. Among solar cells using organic materials, it has the advantages that it is high in photovoltaic conversion efficiency and is lower in manufacturing cost compared with silicon-based solar cells and, therefore, is gaining attention as a new type of solar cell. In particular, since no high temperature treatment is required at the time of production like with a crystalline silicon solar cell, there is active research being conducted for development of a flexible film-type dye-sensitized solar cell.